RE: [CAD_CAM_EDM_DRO] Does this make sense? was Re: Bent Nookballscrews ?????

The one's that are somewhat open-minded and willing to listen and take
advice.

> -----Original Message-----
> From: Vince Negrete [mailto:vnegrete@...]
> Sent: Tuesday, August 12, 2003 12:27 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Does this make sense? was Re: Bent
> Nookballscrews ?????
>
>
> I've worked many years with this type of repetitious conversation, between
> Ivy-League Engineers Fired up on Expresso and Laymen in the field working
> with the hardware for 30 years. I came to the conclusion many years ago
> that its really a waste of precious time and talent.
>
> In the company I work for they Layed off over 4500 people.. Take a guess
> what type of Engineers and Technicians they kept...
>
>
> ----- Original Message -----
> From: "Kim Lux" <lux@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Tuesday, August 12, 2003 8:00 AM
> Subject: Re: [CAD_CAM_EDM_DRO] Does this make sense? was Re: Bent
> Nookballscrews ?????
>
>
> > On Tue, 2003-08-12 at 08:26, ballendo wrote:
> > > Kim,
> > >
> > > I believe that John is correct, and you are misunderstanding some
> > > things... To begin with, let's assume a perfect thread in the
> > > ballscrew and ballnut. Now let's put a non-compliant spacer between
> > > the two nuts which is exactly the correct length to place the balls
> > > into a zero clearance relationship with the threads of the nut and
> > > screw.(which we can do in this example due to the perfect threads)
> >
> > OK.
> >
> > > This totally non backlash system will have the ability to withstand
> > > axial forces up to the material deformation level of the nut and
> > > screw threadform(s) and balls. And MORE importantly, it will add
> > > NOTHING to the rotational force required to turn the screw.
> >
> > OK
> >
> > > Now in the real world, threadforms are not perfect, and spacers of
> > > exact length are not often possible, except with extremely accurate
> > > screws which will ALWAYS be of at least a ground precision type.
> >
> > Sure. Lets assume that we've got our ballnut adjusted to be but snug on
> > the most divergent 3" of the thread. Thus, there will be areas on the
> > screw where the backlash nut is loose. See comments below for what
> > happens in the real world.
> >
> > > So instead of adding zero to the rotational torque required, a SMALL
> > > additional force is required. This allows the balls to be preloaded,
> > > which means they have LESS than zero clearance. (They are deformed
> > > slightly, intentionally.) The threadform of the screw and nut is also
> > > deformed by this preloading. It is this deformation which increases
> > > the rotational force required over the perfect theoretical ideal
> > > described above. And remember, that had NO additional torque required
> > > up to the material deformation limit.
> > >
> > > The degree to which the torque required to turn the screw increases
> > > is based on the quality and consistency of the ball size, threadform,
> > > and lead(pitch). The balls need to be preloaded to the worst case
> > > variation in the combination of these three items.
> >
> >
> > The degree of torque required to turn the ballscrew is defined by an
> > equation. There is a direct mathematical relationship between the axial
> > force on the ballscrew and the torque required to turn it. This
> > relationship is governed by friction, thread pitch, etc. The preload
> > put on the ballnuts is one of these axial forces.
> >
> > > Therefore, when modern, high accuracy machines are made, they use
> > > ground screws so that a lower level of preload is required (resulting
> > > in a non-backlash system with added motor torque required along the
> > > lines of what Jon E said). Our commonly used rolled screws WILL
> > > absorb more rotational force to deal with the variations.
> >
> > NO. THIS IS WRONG. The mathematical equation describes the
> > relationship between axial loads and torque. Preload is an axial load,

> > pure and simple. Torque = axial load x constant, pure and simple.
> >
> >
> > > But you
> > > will find that this comes nowhere near what you have proposed...
> >
> > 1000 pounds of axial load, whether from preload or from cutting load
> > takes 30ish inlbs of torque, no matter how you slice it.
> >
> > > I have personally used this deformation capability to my benefit
> > > (following Dan Mauchs' lead) by buying a SINGLE ballnut, and
> > > reloading it with slightly bigger balls to make it non-backlash.
> >
> > I know nothing about this technique and can't comment.
> >
> > > Carefully done, and carefully broken-in, this technique works well
> > > for machines which can tolerate the overall load capability of a
> > > single circuit/path nut. This technique also takes advantage of the
> > > fact that by using a single nut, the variation dealt with at any
> > > given point is less than it would likely be with the two-nut approach.
> >
> > First of all, if this worked then the ball screw manufacturers would be
> > doing it. Secondly, are you sure it is zero backlash ? Have you
> > measured it with dial indicators with enough load to induce backlash ?
> > We've measured our zero backlash setup and it is truly zero backlash,
> > even under loads, with a 0.0001" dial indicator.
> >
> > With the two ballnut preloaded system, some people are worried about the
> > ballnuts jamming on sections of the ballscrew with a narrower or wider
> > pitch. In practices, this hasn't been a problem. I suspect that there
> > is very, very little pitch variation in a rolled or ground ballscrew (we
> > have both) but what drives the error spec the ballscrew manufacturers
> > quote is the gross error in the lead over a distance. Ie when they
> > quote 5 TPI or 60 TPfoot, we really get 60 threads in 12.004" instead of
> > 12.000 inches. If one runs a tightened zero backlash ballnut assembly
> > over a length of ballscrew, there are no tight spots and we've been
> > unable to detect any backlash anywhere on the screw.
> >
> >
> > > Hope this helps,
> > >
> > > Ballendo
> > >
> > > P.S. Certainly there are MANY high quality machines out there making
> > > parts with the belleville washer type dual nut anti-backlash setup;
> > > as this was the defacto standard in the industry until the wider
> > > availability of cheaper, better quality thread grinding machines made
> > > ground screws more common, and more accurate (for a given price).
> > > Which made the use of non-compliant spacers more common on high
> > > quality machines made today.
> >
> >
> > Our two ballnut system is a version of the non compliant spacer setup.
> >
> > > P.P.S. Part of the calculations necessary to use ballscrews properly
> > > is to choose a size which allows the material of the nut, screw, and
> > > balls to withstand the necessary loads/forces... In other words, if
> > > your load requirements are high you use a larger ball size(or more
> > > balls/circuits) to handle the load without exceeding the elastic
> > > limit of the material. (Also compression strength of the screw, but
> > > that is not pertinent to this specific discussion.)
> >
> > Agreed. Why are you stating this ?
> >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:
> > > >
> > > > Comments below.
> > > >
> > > > On Mon, 2003-08-11 at 22:24, Jon Elson wrote:
> > > > > Kim Lux wrote:
> > > > >
> > > > > >A substantial amount of force would have to be greater than the
> > > pushin
> > > > > >capacity of the motor so that there was never a force that would
> > > > > >displace the nuts against each other. If the spring is weaker
> > > than the
> > > > > >pushing force of the motor, then it will displace the backlash
> > > under a
> > > > > >heavy cut.
> > > > > >
> > > > > >As soon as the nuts are adjusted for the maximum force the motor
> > > is
> > > > > >capable of moving, there isn't any force left to move the
> > > cutter.
> > > > > >
> > > > > >
> > > > > No, you're confusing drag with linear thrust.
> > > >
> > > > No, I'm pretty sure I'm not. Lets say we have an axis that needs,
> > > on
> > > > occasion, 500 lbs of cutting force. In order to ensure that we
> > > never
> > > > had backlash, we'd have to put a preload and the backlash nut of 500
> > > > lbs, to keep the backlash zero in the presence of our load. That
> > > then
> > > > puts the load on the ballscrew at 1000 lbs, ie 500lbs for the
> > > cutting
> > > > load and 500 lbs for the backlash.
> > > >
> > > > > If the system is designed to
> > > > > apply 1000 Lbs of linear thrust, you want somewhat over 1000 Lbs
> > > > > of preload force between the two ballnuts.
> > > >
> > > > Yes. Thus the total load on that ballscrew is 2000 lbs. It takes
> > > twice
> > > > the motor to turn the preloaded system.
> > > >
> > > > > On a good ground screw,
> > > > > 1000 Lbs of preload will cause a very mild drag, maybe 10 Oz-In
> > > > > when new, and decreasing as the screw and nuts wear in a little.
> > > >
> > > > Where do you get your information from ? A 3/4" 5 TPI ballscrew
> > > has a
> > > > force to torque ratio of about 31 lbs force per in pound of torque.
> > > > 1000lbs/31 inlbs/lb = 32ish inlbs of torque or 516 oz in of torque,
> > > just
> > > > to turn the backlash preload on the nuts.
> > > >
> > > > > You don't have to adjust the nuts until they bind up. That could
> > > be
> > > > > 5000 - 10,000 Lbs of preload, and will quickly destroy the balls.
> > > >
> > > > HUH ?
> > > >
> > > >
> > > > >
> > > > > Jon
> > > > >
> > > > >
> > > > > Addresses:
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> > > > >
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> > > > --
> > > > Kim Lux <lux@d...>
> > >
> > >
> > > Addresses:
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> > >
> > > OFF Topic POSTS: General Machining
> > > If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com to
> reach it if
> you have trouble.
> > > http://www.metalworking.com/news_servers.html
> > >
> > > http://groups.yahoo.com/group/jobshophomeshop I consider
> this to be a
> sister site to the CCED group, as many of the same members are
> there, for OT
> subjects, that are not allowed on the CCED list.
> > >
> > > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY
> POSTING THEM.
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> > > bill
> > > List Mom
> > > List Owner
> > >
> > >
> > >
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> > --
> > Kim Lux <lux@...>
> >
> > Addresses:
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> >
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> >
> > OFF Topic POSTS: General Machining
> > If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com to
> reach it if
> you have trouble.
> > http://www.metalworking.com/news_servers.html
> >
> > http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
> sister site to the CCED group, as many of the same members are
> there, for OT
> subjects, that are not allowed on the CCED list.
> >
> > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
> DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> > bill
> > List Mom
> > List Owner
> >
> >
> >
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you have trouble.
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http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.

NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
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